Process to Prepare a Lubricating Base Oil

ABSTRACT

Process to prepare a base oil having an paraffin content of between 75 and 95 wt % by subjecting a mixture of a Fischer-Tropsch derived feed and a petroleum derived feed to a catalytic pour point reducing treatment.

The invention is directed to a process to prepare a base oil having anparaffin content of between 75 and 95 wt %.

WO-A-0157166 describes the use of a highly paraffinic base oil asobtained from a Fischer-Tropsch wax in a motor engine lubricantformulation. The examples illustrate that such formulations will alsoconsist of an ester, which according to the description of the patentare added to confer additional desired characteristics, such as additivesolvency.

The use of ester co-base fluids in lubricant formulations as illustratedin WO-A-0157166 is not desired because such ester co-base fluids are notwidely available and thus expensive. Additive solvency may be improvedby using a paraffinic base stock, which contains less paraffins. Suchbase oils may be prepared by hydroisomerisation of petroleum derivedwaxes followed by a solvent or catalytic dewaxing step. A disadvantageof such a process is that the starting petroleum derived waxes, such asfor example slack wax, are not easily obtainable. Furthermore such waxesmay not always have the desired high paraffin content needed to make thedesired base oils as per this invention.

The object of the present invention is to provide a process wherein abase oil with a paraffin content of between 75 and 95 wt % is obtainedwhich does not have the disadvantages of the prior art processes.

This object is achieved by the following process. Process to prepare abase oil having an paraffin content of between 75 and 95 wt % bysubjecting a mixture of a Fischer-Tropsch derived feed and a petroleumderived feed to a catalytic pour point reducing treatment.

Applicants found that by mixing a relatively small amount of a petroleumderived feed with a Fischer-Tropsch derived feed before performing acatalytic pour point reducing treatment a base oil may be obtainedhaving the desired properties.

The petroleum-derived fraction may in principle be any fraction boilingin the base oil range and containing non-paraffinic compounds.Preferably a petroleum-derived fraction is used which has been subjectedto a hydroprocessing step in order to reduce aromatic, sulphur andnitrogen content of such fractions and improve some of the desiredproperties such viscosity index. The hydroprocessing step may be ahydrotreating optionally followed by a hydrocracking step. Suchprocesses are for example performed when preparing base oils from apetroleum derived vacuum distillate or de-asphalted oils.

A very interesting petroleum derived feed is the bottoms fraction of afuels hydrocracker. With a fuels hydrocracker in the context of thepresent invention is meant a hydrocracker process which main productsare naphtha, kerosene and gas oil. The conversion, expressed in theweight percentage of the fraction in the feed to thehydrotreater-hydrocracker which boils above 370° C. which are convertedto products boiling below 370° C., in the hydrotreater-hydrocrackerprocess is typically above 50 wt %. Examples of possible fuelshydrocracker processes, which may yield a bottoms fraction which can beused in the present process, are described in the above referred toEP-A-699225, EP-A-649896, WO-A-9718278, EP-A-705321, EP-A-994173 andU.S. Pat. No. 4,851,109.

Another interesting petroleum derived feed is the fraction obtained in adedicated base oil hydrotreater-hydrocracker. In such ahydrotreater-hydrocracker the main products will boil in the base oilrange. Typically such processes operate at a feed conversion of below 50wt % and more typically between 20 and 40 wt %. The petroleum derivedfeed is thus the high boiling fraction as obtained in such a processprior to dewaxing.

Preferably the fuels hydrocracker is operated in two steps, consistingof a preliminary hydrotreating step followed by a hydrocracking step. Inthe hydrotreating step nitrogen and sulphur are removed and aromaticsare saturated to naphthenes

The Fischer-Tropsch derived feed preferably is a hydroisomerizedFischer-Tropsch wax. Such a feed may be obtained by well-knownprocesses, for example the so-called commercial Sasol process, the ShellMiddle Distillate Process or by the non-commercial Exxon process. Theseand other processes are for example described in more detail inEP-A-776959, EP-A-668342, U.S. Pat. No. 4,943,672, U.S. Pat. No.5,059,299, WO-A-9934917 and WO-A-9920720. The process will generallycomprise a Fischer-Tropsch synthesis and a hydroisomerisation step asdescribed in these publications.

The mixture of petroleum derived and Fischer-Tropsch derived feeds willsuitably have a viscosity corresponding to the desired viscosity of thebase oil product. Preferably the kinematic viscosity at 100° C. of themixture is between 3 and 10 cSt. Suitable distillate fractions obtainedin step (a) have a T10 wt % boiling point of between 200 and 450° C. anda T90 wt % boiling point of between 300 and 550° C. The fraction ofpetroleum derived feed in the mixture is preferably higher than 5 wt %,more preferably higher than 10 wt % and preferably lower than 50 wt %and more preferably below 30 wt % and even more preferably below 25 wt%. The actual content of petroleum-derived feed in the mixture will ofcourse depend on the paraffin content of said feed. The mixture willpreferably contain less than 50 ppm sulphur and/or less that 10 ppmnitrogen.

With the catalytic pour point reducing treatment is understood everyprocess wherein the pour point of the base oil is reduced by more than10° C., preferably more than 20° C., more preferably more than 25° C.

The catalytic dewaxing or pour point reducing process can be performedby any process wherein in the presence of a catalyst and hydrogen thepour point of the base oil precursor fraction is reduced as specifiedabove. Suitable dewaxing catalysts are heterogeneous catalystscomprising a molecular sieve and optionally in combination with a metalhaving a hydrogenation function, such as the Group VIII metals.Molecular sieves, and more suitably intermediate pore size zeolites,have shown a good catalytic ability to reduce the pour point of thedistillate base oil precursor fraction under catalytic dewaxingconditions. Preferably the intermediate pore size zeolites have a porediameter of between 0.35 and 0.8 nm. Suitable intermediate pore sizezeolites are mordenite, ZSM-5, ZSM-12, ZSM-22, ZSM-23, SSZ-32, ZSM-35and ZSM-48. Another preferred group of molecular sieves are thesilica-aluminaphosphate (SAPO) materials of which SAPO-11 is mostpreferred as for example described in U.S. Pat. No. 4,859,311. ZSM-5 mayoptionally be used in its HZSM-5 form in the absence of any Group VIIImetal. The other molecular sieves are preferably used in combinationwith an added Group VIII metal. Suitable Group VIII metals are nickel,cobalt, platinum and palladium. Examples of possible combinations areNi/ZSM-5, Pt/ZSM-23, Pd/ZSM-23, Pt/ZSM-48 and Pt/SAPO-11. Furtherdetails and examples of suitable molecular sieves and dewaxingconditions are for example described in WO-A-9718278, U.S. Pat. No.5,053,373, U.S. Pat. No. 5,252,527 and U.S. Pat. No. 4,574,043.

The dewaxing catalyst suitably also comprises a binder. The binder canbe a synthetic or naturally occurring (inorganic) substance, for exampleclay, silica and/or metal oxides. Natural occurring clays are forexample of the montmorillonite and kaolin families. The binder ispreferably a porous binder material, for example a refractory oxide ofwhich examples are: alumina, silica-alumina, silica-magnesia,silica-zirconia, silica-thoria, silica-beryllia, silica-titania as wellas ternary compositions for example silica-alumina-thoria,silica-alumina-zirconia, silica-alumina-magnesia andsilica-magnesia-zirconia. More preferably a low acidity refractory oxidebinder material which is essentially free of alumina is used. Examplesof these binder materials are silica, zirconia, titanium dioxide,germanium dioxide, boria and mixtures of two or more of these of whichexamples are listed above. The most preferred binder is silica.

A preferred class of dewaxing catalysts comprise intermediate zeolitecrystallites as described above and a low acidity refractory oxidebinder material which is essentially free of alumina as described above,wherein the surface of the aluminosilicate zeolite crystallites has beenmodified by subjecting the aluminosilicate zeolite crystallites to asurface dealumination treatment. A preferred dealumination treatment isby contacting an extrudate of the binder and the zeolite with an aqueoussolution of a fluorosilicate salt as described in for example U.S. Pat.No. 5,157,191 or WO-A-2000029511. Examples of suitable dewaxingcatalysts as described above are silica bound and dealuminated Pt/ZSM-5,silica bound and dealuminated Pt/ZSM-23, silica bound and dealuminatedPt/ZSM-12, silica bound and dealuminated Pt/ZSM-22 as for exampledescribed in WO-A-200029511 and EP-B-832171.

Catalytic dewaxing conditions are known in the art and typically involveoperating temperatures in the range of from 200 to 500° C., suitablyfrom 250 to 400° C., hydrogen pressures in the range of from 10 to 200bar, preferably from 40 to 70 bar, weight hourly space velocities (WHSV)in the range of from 0.1 to 10 kg of oil per litre of catalyst per hour(kg/l/hr), suitably from 0.2 to 5 kg/l/hr, more suitably from 0.5 to 3kg/l/hr and hydrogen to oil ratios in the range of from 100 to 2,000litres of hydrogen per litre of oil. By varying the temperature between315 and 375° C. at between 40-70 bars, in the catalytic dewaxing step itis possible to prepare base oils having different pour pointspecifications varying from suitably lower than −60 to −10° C.

After performing the pour point reducing treatment lower boilingcompounds formed during said treatment are suitably removed, preferablyby means of distillation, optionally in combination with an initialflashing step.

The effluent of the pour point reducing treatment may suitably besubjected to a hydrogenation treatment. Hydrogenation may be performedon the entire effluent or on specific base oil grades after the abovedescribed fractionation. This may be required in order to reduce thecontent of aromatic compounds in the reduced pour point product topreferably values of below 1 wt %. Such a hydrogenation is also referredto as a hydrofinishing step. This step is suitably carried out at atemperature between 180 and 380° C., a total pressure of between 10 to250 bar and preferably above 100 bar and more preferably between 120 and250 bar. The WHSV (Weight hourly space velocity) ranges from 0.3 to 2 kgof oil per litre of catalyst per hour (kg/l·h). Preferably ahydrogenation is performed in the same reactor as the catalytic dewaxingreactor. In such a reactor the beds of dewaxing catalyst andhydrogenation catalyst will be placed in a stacked bed on top of eachother.

The hydrogenation catalyst is suitably a supported catalyst comprising adispersed Group VIII metal. Possible Group VIII metals are cobalt,nickel, palladium and platinum. Cobalt and nickel containing catalystsmay also comprise a Group VIB metal, suitably molybdenum and tungsten.Suitable carrier or support materials are low acidity amorphousrefractory oxides. Examples of suitable amorphous refractory oxidesinclude inorganic oxides, such as alumina, silica, titania, zirconia,boria, silica-alumina, fluorided alumina, fluorided silica-alumina andmixtures of two or more of these.

Examples of suitable hydrogenation catalysts are nickel-molybdenumcontaining catalyst such as KF-847 and KF-8010 (AKZO Nobel) M-8-24 andM-8-25 (BASF), and C-424, DN-190, HDS-3 and HDS-4 (Criterion);nickel-tungsten containing catalysts such as NI-4342 and NI-4352(Engelhard) and C-454 (Criterion); cobalt-molybdenum containingcatalysts such as KF-330 (AKZO-Nobel), HDS-22 (Criterion) and HPC-601(Engelhard). Preferably platinum containing and more preferably platinumand palladium containing catalysts are used. Preferred supports forthese palladium and/or platinum containing catalysts are amorphoussilica-alumina. Examples of suitable silica-alumina carriers aredisclosed in WO-A-9410263. A preferred catalyst comprises an alloy ofpalladium and platinum preferably supported on an amorphoussilica-alumina carrier of which the commercially available catalystC-624 of Criterion Catalyst Company (Houston, Tex.) is an example.

From the effluent of the pour point reducing treatment and the optionalhydrogenation treatment one or more base oil grades may be isolated bymeans of fractionation. Base oil products having kinematic viscosity at100° C. of between 2 and 10 cSt, having a volatility of between 8 and11% (according to CEC L40 T87) and a pour point of between −20 and −60°C. (according to ASTM D 97) may advantageously be obtained.

The content of paraffins is more preferably less than 90 wt % and morepreferably higher than 80 wt %.

The above-described base oil can suitably find use as base oil for anAutomatic Transmission Fluids (ATF), motor engine oils, electrical oilsor transformer oils and refrigerator oils. lubricant formulations suchas motor engine oils of the 0W-x and 5W-x specification according to theSAE J-300 viscosity classification, wherein x is 20, 30, 40, 50 or 60may be advantageously made using this base oil.

It has been found that lubricant formulations can be prepared with thebase oils obtainable by the process of the current invention without theneed to add high contents of additional ester or aromatic co-base oils.Preferably less than 15 wt % and more preferably less than 10 wt % ofsuch ester or aromatic co-base oil is present in such formulations.

1. A process to prepare a base oil having a paraffin content of between75 and 95 wt % the process comprising subjecting a mixture of ahydroisomerized Fischer-Tropsch wax and a petroleum derived feed to acatalytic pour point reducing treatment, wherein the petroleum derivedfeed has an aromatic content of between 0 and 20 wt % and a naphtheniccompound content of between 15 and 90 wt % and wherein the fraction ofpetroleum derived feed in the mixture is higher than 5 wt % and lowerthan 50 wt %.
 2. The process of claim 1, wherein the petroleum derivedfeed is a bottoms fraction of a fuels hydrocracker.
 3. The process ofProcess according to claim 2, wherein the content of sulfur in the mixedfeed to the pour point reducing treatment is below 50 ppm and thecontent of nitrogen in the mixed feed to the pour point reducingtreatment is below 10 ppm.
 4. The process of claim 1, wherein the waxcontent in the petroleum derived feed is below 30 wt %.
 5. The processof claim 4, wherein the pour point of the petroleum derived feed isbelow −10° C.
 6. The process of claim 1, wherein the petroleum derivedfeed has a saturates content of greater than 98 wt % a viscosity indexof between 80 and 150 and a sulfur content of below 0.001 wt %.
 7. Theprocess of claim 6, wherein the petroleum derived feed has been obtainedin a process comprising a hydrofinishing step performed at a hydrogenpressure of greater than 100 bars.
 8. The process of claim 1, whereinthe base oil is hydrogenated after performing the pour point reducingtreatment such that the content of aromatics is below 1 wt %.
 9. Theprocess of claim 1, wherein the catalytic pour point reducing treatmentis a catalytic dewaxing process performed in the presence of a catalystcomprising a Group VIII metal and an intermediate pore size zeolitehaving pore diameter between 0.35 and 0.8 nm, and a binder.
 10. Theprocess of claim 1, wherein after performing the catalytic pour pointreducing treatment hydrogen is separated from the dewaxed effluent,contacted with a heterogeneous adsorbent selective for removing hydrogensulfide and recycled to said catalytic pour point reducing treatment.11. The process of claim 10, wherein the heterogeneous adsorbent is zincoxide.
 12. The process of claim 1, wherein the hydroisomerizedFischer-Tropsch wax is obtained by a process comprising: (a)hydrocracking/hydroisomerizing a Fischer-Tropsch product, and, (b)distilling the product of step (a) into one or more gas oil fractionsand a higher boiling Fischer-Tropsch derived feed.
 13. The process ofclaim 12, wherein the Fischer-Tropsch product used as feed in step (a)is a product wherein the weight ratio of compounds having at least 60 ormore carbon atoms and compounds having at least 30 carbon atoms in theFischer-Tropsch product is at least 0.4 and wherein at least 30 wt % ofcompounds in the Fischer-Tropsch product have at least 30 carbon atoms.14. The process of claim 2, wherein the content of sulfur in the mixedfeed to the pour point reducing treatment is below 50 ppm and thecontent of nitrogen in the mixed feed to the pour point reducingtreatment is below 10 ppm.
 15. The process of claim 2, wherein the waxcontent in the petroleum derived feed is below 30 wt %.
 16. The processof claim 15, wherein the pour point of the petroleum derived feed isbelow −10° C.
 17. The process of claim 2, wherein the petroleum derivedfeed has a saturates content of greater than 98 wt % a viscosity indexof between 80 and 150 and a sulfur content of below 0.001 wt %.
 18. Theprocess of claim 17, wherein the petroleum derived feed has beenobtained in a process comprising a hydrofinishing step performed at ahydrogen pressure of greater than 100 bars.
 19. The process of claim 2,wherein the base oil is hydrogenated after performing the pour pointreducing treatment such that the content of aromatics is below 1 wt %.20. The process of claim 2, wherein the catalytic pour point reducingtreatment is a catalytic dewaxing process performed in the presence of acatalyst comprising a Group VIII metal and an intermediate pore sizezeolite having pore diameter between 0.35 and 0.8 nm, and a binder. 21.The process of claim 2, wherein after performing the catalytic pourpoint reducing treatment hydrogen is separated from the dewaxedeffluent, contacted with a heterogeneous adsorbent selective forremoving hydrogen sulfide and recycled to said catalytic pour pointreducing treatment.
 22. The process of claim 21, wherein theheterogeneous adsorbent is zinc oxide.
 23. The process of claim 2,wherein the hydroisomerized Fischer-Tropsch wax is obtained by a processcomprising: (a) hydrocracking/hydroisomerizing a Fischer-Tropschproduct, and, (b) distilling the product of step (a) into one or moregas oil fractions and a higher boiling Fischer-Tropsch derived feed. 24.The process of claim 23, wherein the Fischer-Tropsch product used asfeed in step (a) is a product wherein the weight ratio of compoundshaving at least 60 or more carbon atoms and compounds having at least 30carbon atoms in the Fischer-Tropsch product is at least 0.4 and whereinat least 30 wt % of compounds in the Fischer-Tropsch product have atleast 30 carbon atoms.